Liquid crystal alignment agent, film and display element

Abstract

A liquid crystal alignment agent includes a polymer and an organic solvent for dissolving the polymer. The polymer contains a repeating structural unit represented by the following formula (I): wherein each of P and Q is a divalent organic group. The liquid crystal alignment agent has a viscosity in the range from 5 to 40 cps at 25° C. A liquid crystal alignment film made of the liquid crystal alignment agent and a liquid crystal display element including the liquid crystal alignment film are also disclosed.

What is claimed is: 
     
       1. A liquid crystal alignment agent, comprising:
 a polymer containing a repeating structural unit represented by the following formula (I): 
 
       
         
           
           
               
               
           
         
         wherein each of P and Q is a divalent organic group; and 
         an organic solvent for dissolving said polymer, wherein the liquid crystal alignment agent has a viscosity ranging from 8 to 35 cps at 25° C., 
         wherein said polymer is obtained by subjecting a diamine compound to polymerization in the presence of an acidic catalyst, and 
         wherein said diamine compound is at least one selected from the group consisting of compounds represented by the following formulas (I-1) to (I-5) and (1) to (6): 
       
       
         
           
           
               
               
           
         
       
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
       
       wherein
 R 3  is a monovalent organic group having a ring structure containing a nitrogen atom selected from the group consisting of pyridine, pyrimidine, triazine, piperidine and piperazine; 
 X is a divalent organic group; 
 R 4a  and R 4b  are independently a divalent organic group having a ring structure containing a nitrogen atom selected from the group consisting of pyridine, pyrimidine, triazine, piperidine and piperazine; 
 R 5  and R 7  are independently a divalent organic group selected from the group consisting of —O—, —COO—, —OCO—, —NHCO—, —CONH—, and —CO—; 
 R 6  is a monovalent organic group having a group selected from the group consisting of a steroid skeleton, a trifluoromethyl group, and a fluoro group, or an alkyl group having 6 to 30 carbon atoms; 
 X 1  and X 2  are independently a divalent organic group selected from the group consisting of an alicyclic group, an aromatic group, and a heterocyclic group; 
 R 8  is selected from the group consisting of an alkyl group having 3 to 18 carbon atoms, an alkoxy group having 3 to 18 carbon atoms, a fluoroalkyl group having 1 to 5 carbon atoms, a fluoroalkoxy group having 1 to 5 carbon atoms, a cyano group, and halogen atoms; 
 R 9a , R 9b , R 9c , and R 9d  are independently a hydrocarbon group having 1 to 12 carbon atoms; 
 p is an integer ranging from 1 to 3; 
 q is an integer ranging from 1 to 20; and 
 t is an integer ranging from 2 to 12. 
 
     
     
       2. The liquid crystal alignment agent as claimed in  claim 1 , wherein said organic solvent is in an amount of 400 to 10,000 parts by weight based on 100 parts by weight of said polymer. 
     
     
       3. The liquid crystal alignment agent as claimed in  claim 2 , wherein said organic solvent is in an amount of 500 to 5,000 parts by weight based on 100 parts by weight of said polymer. 
     
     
       4. A liquid crystal alignment film made of the liquid crystal alignment agent as claimed in  claim 1 . 
     
     
       5. A liquid crystal display element, comprising the liquid crystal alignment film as claimed in  claim 4 .